[FEATURE] 当对象中含有BigInteger类型的字段时，没有办法在全局设置中强制转换String

```
@Data
public static class test {
int a = 1;
Integer b = 2;
long c = 1;
Long d = 1123123213213123213L;

//@JSONField(serializeUsing = BigIntegerToStringSerializer.class)
BigInteger e = new BigInteger("123");

}

public static void main(String[] args) {
FastJsonConfig jsonConfig = new FastJsonConfig();
jsonConfig.setWriterFeatures();

ObjectWriterProvider objectWriterProvider=new ObjectWriterProvider();
objectWriterProvider.register(Long.class, ObjectWriters.ofToString(Object::toString));
JSONWriter.Context context= JSONFactory.createWriteContext(objectWriterProvider);

JSON.config(JSONWriter.Feature.WriteLongAsString);

//JSON.config(JSONWriter.Feature.WriteNonStringValueAsString);
//JSON.config(JSONWriter.Feature.BrowserCompatible);

JSON.register(Long.class, ObjectWriters.ofToString(Object::toString));
JSON.register(Long.TYPE, ObjectWriters.ofToString(Object::toString));
JSON.register(BigInteger.class, ObjectWriters.ofToString(Object::toString));

String json1 = JSONObject.toJSONString(new test());

log.info(json1);
}
```

输出结果{"a":1,"b":2,"c":"1","d":"1123123213213123213","e":123}

JSONWriter.Feature.WriteNonStringValueAsString和JSONWriter.Feature.BrowserCompatible虽然能部分实现，但是会引入更多的问题，一个会强制把所有的对象都转为字符串，另一个则是为了适配浏览器兼容只会把超过9007199254740991和小于-9007199254740991的转为string，而且空值还会按 JSON 标准输出 null/undefined

看了下源码，序列化时最终会进入JSONWriterUTF16.writeBigInt方法，其中有个isWriteAsString来判断是否转为String

protected static boolean isWriteAsString(BigDecimal value, long features) {
return (features & MASK_WRITE_NON_STRING_VALUE_AS_STRING) != 0
|| ((features & MASK_BROWSER_COMPATIBLE) != 0 && !isJavaScriptSupport(value));
}

只有JSONWriter.Feature.WriteNonStringValueAsString或者JSONWriter.Feature.BrowserCompatible并且超出了9007199254740991范围才会转String

希望能增加一个JSONWriter.Feature.WriteBigIntegerAsString的枚举和判断条件，或者有其他的方法请告知一下，不胜感激

Start in JSONWriterUTF16.writeBigInt and inspect the isWriteAsString logic described in the issue, along with the JSONWriter.Feature definitions. Add the requested global BigInteger-as-string behavior without changing the broader WriteNonStringValueAsString or BrowserCompatible semantics; done means BigInteger fields serialize as strings when the new setting is enabled.

Written by the indexing model from the issue text.